This invention relates to an imaging element containing a blocked photographically useful compound such as a developing agent.
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film. Developing agents commonly used are reducing agents, for example, p-aminophenols or p-phenylenediamines.
Typically, developing agents (also herein referred to as developers) present in developer solutions are brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film clement has been necessary because the incorporation of developers directly into sensitized photographic elements can lead to desensitization of the silver halide emulsion and undesirable fog (indiscriminate image formation). Considerable effort, however, has been directed to producing effective blocked developing agents (also referred to herein as blocked developers) that might be introduced into silver halide emulsion elements without deleterious desensitization or fog effects. Accordingly, blocked developing agents have been sought that would unblock under preselected conditions of development after which such developing agents would be free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base developer precursors. Schleigh and Faul, in a Research Disclosure (129 (1975) pp. 27-30), describes the quaternary blocking of color developers and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.) Subsequently, U.S. Pat. No. 4,157,915 to Hamaoka et al. and U.S. Pat. No. 4,060,418 to Waxman and Mourning describe the preparation and use of blocked p-phenylenediamines in an image-receiving sheet for color diffusion transfer.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, lack of simple methods for releasing the blocked developer, inadequate or poor image formation, and other problems. Especially in the area of photothermographic color films, other potential problems include poor discrimination and poor dye-forming activity.
There remains a need for blocked photographically useful compounds with good keeping properties, which at the same time exhibit good unblocking kinetics. With respect to developing agents, it is an object to obtain a film incorporating blocked developing agents that provide good dye-forming activity and which, at the same time, yield little or no increased fog and/or provide little or no decrease in Dmax after storage.
It is a further object to obtain blocked photographically useful agents for use in photothermographic color films. In photothermographic systems all of the required imaging materials must be present simultaneously within the film package. That is, the package must contain silver halide, coupler, and developer, a combination of ingredients which, if allowed to react normally, would produce undesirable fog. In developing a color photothermographic film, fog is one of the most pressing problem, particularly during raw stock keeping.
With respect to developing agents, there is a continuing need for photothermographic imaging elements that contain a developing agent in a form that is stable until development yet can rapidly and easily develop the imaging element once processing has been initiated by heating the element and/or by applying a processing solution, such as a solution of a base or acid or pure water, to the element. A completely dry or apparently dry process is most desirable. The existence of such a process would allow for very rapidly processed films that can be processed simply and efficiently in photoprocessing kiosks. Such kiosks, with increased numbers and accessibility, could ultimately allow for, relatively speaking, anytime and anywhere silver-halide film development.
This invention relates to a polymeric heteraromatically-blocked developing agent or compound that decomposes (i.e., unblocks) on thermal activation to release a photographically useful developing agent (also referred to herein as DEV).
In one embodiment, thermal activation preferably occurs at temperatures between about 100 and 180xc2x0 C. In another embodiment, thermal activation preferably occurs at temperatures between about 20 and 140xc2x0 C. in the presence of added acid, base and/or water.
The invention further relates to a light sensitive photographic element comprising a support and a polymeric heteraromatically-blocked developing agent that decomposes on thermal activation to release a photographically useful group.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a polymeric heteraromatically-blocked developing agent that decomposes on thermal activation to form a developed image, scanning said developed image to form a first electronic image representation (or xe2x80x9celectronic recordxe2x80x9d) from said developed image, digitizing said first electronic record to form a digital image, modifing said digital image to form a second electronic image representation, and storing, transmitting, printing or displaying said second electronic image representation.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a polymeric heteraromatically-blocked developing agent that decomposes on thermal activation. The invention further relates to a method of image formation having the steps of imagewise exposing such a light sensitive photographic element in a one-time-use camera having a heater and thermally processing the exposed element in the camera.
The improvements were achieved by a compound containing a five-membered heteroaromatic ring shown in Structure I: 
wherein x indicates the number of the repeat units of Structure I in the polymeric blocked developer.
R is hydrogen or methyl and HET is a heteroaromatic group selected from A, B, C, and D below: 
wherein $ denotes a bond to in the direction of the polymeric backbone (i.e., is a bond to G, W, or the polymeric backbone, whichever is adjacent to HET) and # denotes a bond to C* in the direction of DEV in the above structure;
wherein X is O, S, or NR9 and R1,R2, R9 and n are as defined below; wherein G is either absent or selected from the following group: 
wherein $ denotes the bond in the direction of the polymeric backbone and # denotes a bond to W or HET in the direction of DEV in the above structure I;
R5 (independently in both Structure C and G above) is hydrogen or substituted or unsubstituted alkyl or aryl;
LINK is a linking group;
DEV is a developing agent;
t (subscript) is 0, 1, or 2;
C* is a tetrahedral carbon atom,
R3, and R4 are as defined below,
W is as defined below.